Preheat oven to 325 degrees (F). Put parchment paper on a cookie sheet.

Combine flour, sugar, baking soda, and salt together in a bowl. Cut in the butter (very important, don't skip this) until mixture resembles cornmeal.

Add the almond extract.

Combine white and yolk of egg; add half of it to the bowl. Mix well. The dough will appear too crumbly in the beginning, but when you mix it long enough, it will get the right consistency (that's why you only need half an egg). Reserve remaining half egg.

Roll dough into 1-inch balls. Set them 2 inches apart on the cookie sheet. Press down with your thumb to flatten each cookies slightly. Place an almond slice in the middle of each cookie.

Combine the reserved half of the egg with 1/2 tablespoon water to make a light egg wash glaze. Using a basting brush, cover the tops of the cookies with the glaze. You can adjust the amount of glaze on each cookie depending on how much almond cookie shine you want.

Bake in oven until the the edges of the cookies are golden brown, about 15 to 18 minutes.

Cool on baking sheet for 5 minutes then place on wire rack to cool completely.